Human monocytes have been removed from the peripheral blood of normal volunteers and cancer patients for study in a wide range of immunologic assay systems. The technique of counter-current centrifugal elutriation has been applied to these cells that generate as many as 1 billion 95%-pure monocytes. In addition, lymphocytes that are completely monocyte-depleted can be obtained by the same technology. Elutriation generates monocytes that are in suspension; we've developed techniques to maintain these cells in suspension culture using serum free media and specially developed Teflon labware. Thus, these cultured cells are thought to be most representative of the native state of monocytes in the blood stream. These cells have been studied with regard to their accessory cell function for human lymphocyte activation, their MIF activity, chemotactic activity, ability to release biological response modifiers (including colony stimulating factor, interferon, fibroblast growth factor, prostaglandins and tumor necrosis factor); in addition, the tumoricidal activity of these cells in antibody dependent cytotoxicity and spontaneous cytotoxicity assay systems has been measured. Having documented the tumoricidal activity of elutriator-purified monocytes and our ability to boost this tumor killing capability with gamma-interferon, we have initiated a clinical protocol utilizing large numbers of these cells in an adoptive transfer setting in patients with peritoneal colorectal carcinomatosis. These patients have received weekly administration of their own elutriator-purified monocytes (activated with gamma-interferon) into their peritoneal cavity via an indwelling Tenckhoff catheter. We have shown this therapy to be relatively nontoxic and have developed an outpatient treatment regiment that is very compatible with an active patient lifestyle. We have found that the infused monocytes not only remain in the peritoneal space for prolonged periods of time, but also become integrated into the peritoneal surface itself. The first two patients to complete this trial are currently without evidence of ongoing malignancy.